1. Field of the Invention
The present invention relates to a polyhydroxyalkanoate (PHA) that comprises a novel structural unit and a process for producing the same. More particularly, the present invention relates to a novel biodegradable PHA that comprises 3-hydroxyalkanoic acid units having a (methylsulfanyl)phenoxy group at the end of the side chain thereof, and to a process for producing PHAs from an alkanoic acid having a (methylsulfanyl)phenoxy group at the end of the side chain thereof by using a microorganism capable of producing PHA and accumulating it in the cell.
2. Related Background Art
It has been reported that various microorganisms can produce poly-3-hydroxybutyrate (hereinafter, also referred to as “PHB” for short) or other PHA and accumulate it in the cell (“Biodegradable Plastics Handbook”, Biodegradable Plastics Society Ed., NTS, pages 178-197 (1995)). These polymers may be utilized for production of various products by, for example, melt processing as with conventional plastics, but unlike many conventional synthetic polymer compounds, these polymers do not cause pollution in the natural environment because they are biodegradable, i.e., they are completely degraded by microorganisms in the natural world. Furthermore, they have good biocompatibility and their applications in the medical field as soft materials are expected.
Microbial PHAs are known to have different compositions and/or structures depending on, for example, the type of the microorganism, compositions of the culture medium, and culture conditions. Thus, studies have been done to control the composition and structure to improve physical properties of PHA. For instance, Alcaligenes eutrophus H16 (ATCC No. 17699) and mutants thereof are known to produce copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate (hereinafter, abbreviated as 3HV) with various composition ratios (Japanese Patent Publication No. 6-15604 and Japanese Patent Publication No. 7-14352 and Japanese Patent Publication No. 8-19227).
Japanese Patent No. 2642937 discloses production of PHA of C6 to C12 3-hydroxyalkanoate monomer units by feeding acyclic aliphatic hydrocarbon compounds as substrates to Pseudomonas oleovorans (ATCC No. 29347).
Japanese Patent Application Laid-Open No. 5-7492 discloses a process for producing a copolymer of 3HB and 3HV using a microorganism such as Methylobacterium sp., Paracoccus sp., Alcaligenes sp., and Pseudomonas sp. in contact with C3 to C7 primary alcohol.
Japanese Patent Application Laid-Open No. 5-93049 and Japanese Patent Application Laid-Open No. 7-265065 disclose production of two-component copolymers of 3HB and 3-hydroxyhexanate by cultivating Aeromonas caviae with oleic acid or olive oil as a substrate.
Japanese Patent Application Laid-Open No. 9-191893 discloses that Comamonas acidovorans IFO 13852 produces polyester containing 3HB and 4-hydroxybutyrate as the monomer units when it is cultivated in the presence of gluconic acid and 1,4-butanediol as substrates.
Further, certain microorganisms have already been known to produce PHAs having various substituents introduced such as unsaturated hydrocarbons, ester groups, cyano groups, halogenated hydrocarbons, and epoxides. For example, Macromol. Chem., 191, 1957-1965 (1990), Macromolecules, 24, 5256-5260 (1991), and Chirality, 3, 492-494 (1991) report that Pseudomonas oleovorans produces PHAs containing 3-hydroxy-5-phenylvalerate (hereinafter, abbreviated as 3HPV) as the monomer unit, where changes in physical properties of the PHA are observed probably due to the presence of 3HPV.
Of the PHAs having a substituent on the side chain thereof, lately those having a phenoxy group on the side chain have been actively developed.
It has been reported that Pseudomonas oleovorans produces from 11-phenoxyundecanoic acids PHA made with monomer units of 3-hydroxy-5-phenoxyvalerate and 3-hydroxy-9-phenoxynonanoate (Macromol. Chem. Phys., 195, 1665-1672 (1994)).
Macromolecules, 29, 3432-3435 (1996) reports production of PHA having monomer units of 3-hydroxy-4-phenoxybutyrate and 3-hydroxy-6-phenoxyhexanoate from 6-phenoxyhexanoic acids; production of PHA having units of 3-hydroxy-4-phenoxybutyrate, 3-hydroxy-6-phenoxyhexanoate, 3-hydroxy-4-phenoxybutyrate, 3-hydroxy-6-phenoxyhexanoate and 3-hydroxy-8-phenoxyoctanoate from 8-phenoxyoctanoic acid; and production of PHA made with units of 3-hydroxy-5-phenoxyvaleric acid and 3-hydroxy-7-phenoxyheptanoic acid from 11-hydroxyundecanoic acid, by using Pseudomonas oleovorans. 
Can. J. Microbiol., 41, 32-43 (1995) reports production of PHAs containing 3-hydroxy-6-(4-cyanophenoxy)hexanoic acids or 3-hydroxy-6-(4-nitrophenoxy)hexanoic acid as the monomer units by Pseudomonas oleovorans ATCC 29347 or Pseudomonas putida KT 2422 using octanoic acid and 6-(4-cyanophenoxy)hexanoic acid or 6-(p-nitrophenoxy)hexanoic acid as a substrate.
Recently, PHAs having phenoxy group on the side chain thereof have been actively developed, especially those having functional groups such as fluoro, cyano, and nitro introduced onto the phenoxy aromatic ring of the side chain. Although there are many reports about such PHA, the species are limited to those described above, and no report on PHAs having novel functional groups.